1. Field of the Invention
The present invention relates generally to ultrasonic waveguides and more particularly to an acoustic emission waveguide adapted for physically holding a specimen in a thermally hostile environment and transmitting the acoustic emission response of the specimen through the waveguide to a transducer located in a non-hostile environment.
2. Description of the Prior Art
The present invention is utilizable where a test specimen is to be located in a hostile environment, such as a thermal environment chamber, and it is desired to locate a transducer outside the chamber in a non-hostile environment at room temperature and means are required for guiding ultrasonic energy from the sample to the sensing transducer. The most relevant known prior art is disclosed in U.S. Pat. No. 4,510,812, issued Apr. 16, 1985 to Feng and in U.S. Pat. No. 4,392,380, issued July 12, 1983 to Caines. Both references teach acoustic waveguides utilized where a specimen is to be located in a hostile environment and the transducer is located in a non-hostile environment. These prior art devices both use rather complicated methods of attachment of the specimen to the waveguide.
Feng employs a dry coupling technique utilizing a magnetic mounting fixture, or an adhesively bonded mounting fixture, which holds the tip of the waveguide against the specimen utilizing pressure from a coiled spring. The disclosed device requires either a ferromagnetic surface or one which will not be affected by adhesive bonding. The device is not well suited for low temperature exposures because adhesives are very active sources of acoustic emissions and can mask the emissions from the specimen.
Caines utilizes a U-shaped clamp which surrounds the test specimen and employs a type of dry coupling in which a malleable copper foil is used to make good conformal contact between the test specimen and the tip of the waveguide. This technique requires very high pressure to promote good coupling. Such devices are thus not suited for testing many types of specimens.